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Fri, 13 Dec 2024 06:45:24 -0800 (PST) MIME-Version: 1.0 References: <20240712-asi-rfc-24-v1-0-144b319a40d8@google.com> <20240712-asi-rfc-24-v1-1-144b319a40d8@google.com> <20241025113455.GMZxuCX2Tzu8ulwN3o@fat_crate.local> <878qu6205g.ffs@tglx> <87cyjevgx4.ffs@tglx> In-Reply-To: <87cyjevgx4.ffs@tglx> From: Brendan Jackman Date: Fri, 13 Dec 2024 15:45:13 +0100 X-Gm-Features: AbW1kvYeFSt9oq4jpITmiWkujPAqQ3h82SGc6hTAa_TaGY28cvqrpIH9-qf3xtU Message-ID: Subject: Re: [PATCH 01/26] mm: asi: Make some utility functions noinstr compatible To: Thomas Gleixner Cc: Junaid Shahid , Borislav Petkov , Ingo Molnar , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Sean Christopherson , Paolo Bonzini , Alexandre Chartre , Liran Alon , Jan Setje-Eilers , Catalin Marinas , Will Deacon , Mark Rutland , Andrew Morton , Mel Gorman , Lorenzo Stoakes , David Hildenbrand , Vlastimil Babka , Michal Hocko , Khalid Aziz , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Valentin Schneider , Paul Turner , Reiji Watanabe , Ofir Weisse , Yosry Ahmed , Patrick Bellasi , KP Singh , Alexandra Sandulescu , Matteo Rizzo , Jann Horn , x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, linux-toolchains@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 466E0180003 X-Rspamd-Server: rspam12 X-Stat-Signature: oiasicbu4a58d3sx795h759i891bzg75 X-Rspam-User: X-HE-Tag: 1734101107-978472 X-HE-Meta: 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 TRtGjefL tICpYiXN3MCXHtxJMq6j8MNYNSGOTf4AlxylYT+A4CUgDXy6GTlz1YLhdABWQlia24fg2ETjT1GpEM2bJ/JXzSJyXcIfifqDY15u4jjvpbRuCkXweIJcMhFSLnhmUTLdrJMxeW6+KbVV9kvSnoZjBqZAjSrD0Vsa7px3evFT3LuNhb5k7eycHA1R8ZfwMNxGJOqzQ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000412, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 1 Nov 2024 at 21:27, Thomas Gleixner wrote: > On Thu, Oct 31 2024 at 18:44, Junaid Shahid wrote: > What actually works by some definition of "works" is: > > static __always_inline void __foo(void) { } > > static inline void foo(void) > { > __(foo); > } > > static inline noinstr void foo_noinstr(void) > { > __(foo); > } > > The problem is that both GCC and clang optimize foo[_noinstr]() away and > then follow the __always_inline directive of __foo() even if I make > __foo() insanely large and have a gazillion of different functions > marked noinline invoking foo() or foo_noinstr(), unless I add -fno-inline > to the command line. In this experiment did you modify the definition of noinstr to remove noinline? Otherwise I always get out-of-line calls (as you'd expect from the noinline). > Which means it's not much different from just having '__always_inline > foo()' without the wrappers.... > > Compilers clearly lack a --do-what-I-mean command line option. > > Now if I'm truly nasty then both compilers do what I mean even without a > magic command line option: > > static __always_inline void __foo(void) { } > > static __maybe_unused void foo(void) > { > __(foo); > } > > static __maybe_unused noinstr void foo_noinstr(void) > { > __(foo); > } I don't see any difference with __maybe_unused: if the noinline is there it's never inlined, otherwise with the wrapper technique it's always inlined regardless of __maybe_unused: static __always_inline void __big(void) { asm volatile( "nop; nop; nop; nop; nop; nop; nop; nop; nop;" // and so on "nop; nop; nop; nop; nop; nop; nop; nop; nop;" ); } static inline __section(".noinstr.text") void big_noinstr(void) { __big(); } When I call big_noinstr() from a noinstr function I see: Dump of assembler code for function asi_exit: 0xffffffff811e0080 <+0>: endbr64 0xffffffff811e0084 <+4>: nop 0xffffffff811e0085 <+5>: nop ...and so on I'm using GCC 14.2.0. (I thought maybe this was because I used asm volatile nops to embiggen the function but I see the same thing with a big stream of volatile C statements). I think we might have no choice but to always use __always_inline/noinline for code that's called from both sections - seems there's no way to tell the compiler "I don't care if you inline it, but it we can't cross a section boundary". Am I missing anything?